The delivery of radio frequency (RF) energy to target regions within solid tissue is known for a variety of purposes of particular interest to the present invention. In one particular application, RF energy may be delivered to diseased regions (e.g., tumors) for the purpose of ablating predictable volumes of tissue with minimal patient trauma. RF ablation of tumors is currently performed using one of two core technologies.
The first technology uses a single needle electrode, which when attached to a RF generator, emits RF energy from the exposed, uninsulated portion of the electrode. This energy translates into ion agitation, which is converted into heat and induces cellular death via coagulation necrosis. In theory, RF ablation can be used to sculpt precisely the volume of necrosis to match the extent of the tumor. By varying the power output and the type of electrical waveform, it is theoretically possible to control the extent of heating, and thus, the resulting ablation. The diameter of tissue coagulation from a single electrode, however, is limited by heat dispersion. As a result, multiple probe insertions have been required to treat all but the smallest lesions. This considerably increases treatment duration and requires significant skill for meticulous precision of probe placement.
The second technology utilizes multiple needle electrodes, which have been designed for the treatment and necrosis of tumors in the liver and other solid tissues. U.S. Pat. No. 6,379,353 disclose such a probe. The ablation probe disclosed in U.S. Pat. No. 6,379,353, referred to as the LeVeen Needle Electrode, comprises a cannula having a needle electrode array, which is reciprocatably mounted within the cannula to alternately deploy the electrode array from the cannula and retract electrode array within the cannula. The individual electrodes within the array have spring memory, so that they assume a radially outward, arcuate configuration as they are deployed from the cannula. In general, a multiple electrode array creates a larger lesion than that created by a needle electrode.
Prior to deploying the electrode array, the distal tip of the cannula must first be properly positioned at the ablation site—typically using fluoroscopy. Once the correct position is obtained, the electrode array can be deployed from the cannula, and RF ablation can commence. Due to the inability to accurately image the tip of the cannula, however, site targeting is, at times, difficult using the LeVeen Needle Electrode. In addition, the LeVeen Needle Electrode has an open cannula design, which may be considered traumatic compared to a single needle electrode design.